Before gunman Gene Atkins held dozens of people hostage in a Silver Lake Trader Joe's store in July, he shot his grandmother seven times, kidnapped his girlfriend and led police on a high-speed car chase throughout Los Angeles.

A man haunted by the unsolved murders of his step-grandmother and her friend made a podcast about the crime — it's a story that "48 Hours" started covering as a cold case, but turned into something very different thanks to a relentless detective and cutting-edge technology